Friction Direction: Car Under Own Power vs. Towed

[FireWarden]

Does the direction of friction change based upon where the force is coming from? My brother and I are discussing it...

Specifically...if a car is operating under its own power vs. a car being towed

The two scenarios are such...

A car under its own power...the frictional force is static and positive (forward) because it is opposing the the tires going backward on the road.


For a car being towed...that is where the confusion comes in. Is it the same parameters as above, because the the friction in the opposite direction of the tires moving backwards against the road (because of the force of the towtruck pulling it forward)? The tires are still rotating after all...

Or would the friction be backwards...toward the rear of the car...because it is opposing the overall force of the towtruck moving the car forward...



Any thoughts would be great...

 

[Mu naught]

The direction of the friction is always opposite the direction of motion, or the direction of the net force.

 

[jack action]

The friction force will be opposite to the motion and equal the frictional resistance of the driveline.